Mixed expired nitric oxide in primary pulmonary hypertension in relation to lung diffusion capacity

The mixed expired nitric oxide (NO) production of the lungsof patients with primary pulmonary hypertension (PPH) and normalsubjects was measured to determine the relationship betweenNO production and the diffusion capacity of the lung (KCO).Expired air was collected from eight patients with PPH and 20healthy volunteers for analysis by a chemluminescent analyser.Mean pulmonary artery pressure in the PPH patients was 59.5± 6.45 mmHg and their mean cardiac output was 2.95 ±0.35 l/min. All patients and subjects underwent measurementsof FEV1, VC and KCO. The rate of production of NO in mixed exhaledair was lower in the PPH group compared to the controls (2.85± 0.7 vs. 4.69 ± 0.35 nM/min; p<0.05). Therewas a good correlation of expired NO with the KCO (r=0.7; n=30;p<0.001). When corrected, KCO differences in exhaled NO werenot significant (p=0.09). We conclude that the low exhaled NOobserved in PPH patients is a reflection of the reduced bloodcapillary volume in these patients rather than a decreased basalproduction of NO.